Five years ago the Netherlands was home to a small but healthy population of fire salamanders (Salamandra salamandra terrestris). That is no longer the case. The first dead salamanders, their bodies lacking any visible signs of injuries, turned up in 2008. More mysteriously dead salamanders appeared in the following years, while field surveys found fewer and fewer live animals. By 2011 the number of fire salamanders in the country had dropped by an astonishing 96 percent.

As scientists raced to find the cause behind this mass mortality they brought 39 fire salamanders into captivity, hoping to save the last of the wild animals before they all disappeared. Even that rescue attempt was too late. Half of the captive salamanders were dead by December 2012.

Scientists with the Dutch Wildlife Health Centre and Ghent University in Belgium tested the dead animals (pdf), hoping to find out what had killed them. They ruled out ranavirus, a disease that causes hemorrhaging organs and skin ulcerations in amphibians. Nor did they find Batrachochytrium dendrobatidis (Bd), the deadly chytrid fungus that has spread throughout the world and put many amphibian species on the path toward extinction. The scientists also looked at environmental factors, such as nitrate concentrations. No known agent or infection could be identified.

But now the cause of the fire salamanders' rapid decline has been revealed. According to a paper published today in the Proceedings of the National Academy of Sciences, the fire salamanders in the Netherlands contracted a previously unknown fungus related to Bd, the fungus that causes chytridiomycosis. The paper dubs the new fungus Batrachochytrium salamandrivorans spec. nov. It causes superficial erosions on the salamanders' skin, followed by deep ulcerations and microscopic skin necrosis. Captive-bred amphibians which the scientists exposed to the fungus died in as little as seven days.

"At this moment we don't know the origin of the fungus," says the paper's lead author, An Martel of the Department of Pathology, Bacteriology and Avian Diseases at Ghent University. "It can be an endemic species that became virulent or it can be an invasive species that was introduced in the Netherlands. Worldwide monitoring can give us an answer to this question. But still, if the fungus would spread a lot of amphibian populations are at risk."

This new fungus, which the paper calls "highly pathogenic," occupies a different ecological niche than the previously known Bd. It appears to grow at temperatures as low as 5°C, thrives between 10 and 15 degrees, and dies after five days at temperatures above 25°C. Bd, by comparison, thrives at temperatures between 17 and 25°C. This may limit the salamandrivorans fungus to colder regions such as the Netherlands, but that remains to be seen.

Meanwhile, Martel reports that several other amphibian species co-occur in the fire salamander's habitat in the Netherlands, meaning they too could be at risk. "At this moment, we don't know which species are susceptible to the disease," she says. "This is something that we will investigate in the near future." She suggests the countries neighboring the Netherlands should quickly set up programs to monitor their own populations of fire salamanders and other amphibians. "By doing this, declines will be recognized rapidly and ex situ conservation programs can be set up quickly to prevent the extinction of the species."

The researchers did find two bits of good news. First, several common midwife toads (Alytes obstetricans) exposed to the fungus in the laboratory did not get sick. This suggests the new fungus may not affect as broad of a spectrum of amphibians as Bd. Second, attempts to develop a treatment regime for exposed salamanders show promise. After half of the salamanders that had been rescued from the wild died, the researchers treated the surviving animals with voriconazole, an antifungal medication often used by humans, which appears to been successful. Martel says the salamanders remain healthy today and have even started breeding in captivity. The team is currently working on a protocol to optimize the effectiveness of this treatment.

But the fact that the new fungus was found in the Netherlands and nearly wiped out all of the country's fire salamanders should be cause for international concern, says Kerry Kriger, founder of the nonprofit Save the Frogs and an expert on the chytrid fungus. "The Netherlands is a known hub of the black-market amphibian pet trade. Amsterdam in particular is an entry point for poison dart frogs that are illegally exported out of South America destined for the pet trade." He says future studies should look into this black-market activity and seek to identify the prevalence of the salamandrivorans fungus in the European pet trade. Kriger also calls the new study "an alarm call" for government agencies to legislate the transportation of amphibians, as commerce has allowed the Bd fungus has spread around the world over the past three decades. "Humans ship approximately 100 million amphibians intercontinentally each year, for use in the pet, food, bait, laboratory and zoo trades, with few regulations in place regarding disease testing or quarantines," he says.

Bd has spread to dozens of counties and may have caused more than 100 amphibian extinctions since the 1970s. We can only hope that this new fungus does not add to the ongoing amphibian extinction crisis.

The views expressed are those of the author(s) and are not necessarily those of Scientific American.

ABOUT THE AUTHOR(S)

John R. Platt

John R. Platt is the editor of The Revelator. An award-winning environmental journalist, his work has appeared in Scientific American, Audubon, Motherboard, and numerous other magazines and publications. His "Extinction Countdown" column has run continuously since 2004 and has covered news and science related to more than 1,000 endangered species. John lives on the outskirts of Portland, Ore., where he finds himself surrounded by animals and cartoonists.

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